1. Field of the Invention
The present invention relates to a stage having an electrostatic chuck and used for attracting and holding a target substrate when the target substrate such as a semiconductor wafer is subjected to a process such as etching or film formation and to a plasma processing apparatus using this stage.
2. Description of the Related Art
In a processing apparatus such as a plasma etching apparatus in which semiconductor wafers are processed one by one, a susceptor functioning as a lower electrode is arranged in a process chamber capable of being set in a vacuum state. A wafer serving as a target substrate is placed and fixed on the susceptor, and is subjected to processing. As a means for fixing the wafer on the susceptor, a mechanical holding means such as a clamp and an electrostatic chuck for attracting and holding the wafer by Coulomb's force generated by static electricity are mainly used.
U.S. Pat. No. 4,771,730 (issued on Sep. 20, 1988) discloses an electrostatic chuck arranged on a susceptor or table for supporting a target substrate, e.g., a semiconductor wafer. The electrostatic chuck comprises two dielectric layers and an electrode interposed therebetween. The electrode is connected to the positive terminal of an external DC power supply. In addition, in order to efficiently transfer cold given to the susceptor to the wafer to control the temperature of the wafer, a heat transfer gas is supplied between the lower surface of the wafer and the upper dielectric layer of the electrostatic chuck.
A plurality of vertical holes are formed in the dielectric layers and electrode of the electrostatic chuck to supply the heat transfer gas. A plurality of vertical holes are formed in the susceptor to correspond to the vertical holes of the electrostatic chuck. A plurality of horizontal holes are formed inside the susceptor in a matrix form, a group of vertical holes arranged in a line communicate with one of the horizontal holes. The plurality of horizontal holes communicate with each other, and a supply line extending from, a heat transfer gas source is connected to one portion of the horizontal holes.
The relationship between the vertical and horizontal holes in the susceptor is disclosed in U.S. Pat. No. 5,155,331 (issued on Oct. 13, 1992), though the apparatus disclosed in this patent uses a clamp in place of an electrostatic chuck.
However, side openings must be formed in the side surface of the susceptor to form the vertical and horizontal holes in the susceptor. Furthermore, these side openings must be finally sealed by a certain means. For this reason, formation of the susceptor is cumbersome, and the structure of the susceptor is complicated. Since heat loaded on the susceptor largely varies, the sealed opening may cause leakage of the heat transfer gas due to the influence of thermal expansion and contraction of the susceptor. An adhesive resistant to vacuum which is available at present for sealing such openings is vitrified at a temperature of, e.g., about -80.degree. C., and its sealing function is degraded. If leakage of the heat transfer gas exceeds, e.g., 1 sccm, an etching selectivity is decreased.
When the vertical and horizontal holes have a complicated structure, the conductance of a supply path for the heat transfer gas is decreased, and a pressure reducing speed obtained when an initial low pressure is set before the wafer is placed is easily decreased. The complicated vertical and horizontal holes are easily clogged with a deposit, and the deposit is peeled to form particles in a processing atmosphere.